Isaac approaching hurricane strength

By: Angela Fritz , 9:14 PM GMT on August 27, 2012

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Isaac is walking the line of hurricane status this afternoon after a hurricane hunter mission investigated the storm and found winds of 80+ mph with the SFMR instrument, which looks down at the surface from the plane and estimates what wind speeds are. This instrument has a notoriously rough time in doing so when there's heavy rain, and since the strongest winds were recorded coinciding with the strongest rain, you can imagine that this region of high wind speed could be suspect. The hurricane hunter mission is still in the storm, so I imagine they will issue a special update if needed. Currently the best estimate of wind speed within the storm is 70 mph. Isaac's pressure has been dropping today as well and is now 981 mb. Isaac is moving northwest at 12 mph--no change since this morning. Satellite loops show that Isaac remains large, though asymmetric, with most of the strong thunderstorm activity on the west and southwest side. Isaac's southeast side continues to struggle with dry air and wind shear, which could help to moderate Isaac's intensity as it approaches the coast.

An oil platform in the northern Gulf of Mexico is reporting sustained winds from the north-northeast at 40 mph this afternoon. A buoy west of Tampa, Florida is recording sustained winds around 30 mph, and platforms south of Louisiana are recording winds from 35-40 mph. The widespread heavy rain of yesterday has lightened up in Florida, but a strong line of thunderstorms in one of Isaac's outer bands is training northward along and offshore of the east coast of Florida, affecting everyone from Miami to Jacksonville.

This afternoon the AP reported that Isaac's death toll in Haiti jumped to 19, which puts Isaac's total death count at 21. It appears most of the deaths in Haiti were due to collapsing structures.


Figure 1. Satellite imagery of Tropical Storm Isaac around 3pm EDT on Monday.

Track forecast:
Models seem to be coming into better agreement today on where Isaac will make landfall, closing in on Louisiana and New Orleans as most likely landfall point. The ECMWF, HWRF, and UKMET all suggest New Orleans as the landfall location. The GFS is only slightly west of that. The GFDL is the farthest west, predicting landfall near the Louisiana-Texas border. Landfall timing remains Tuesday night. Beyond landfall, Isaac is expected to move north toward the Midwest through the rest of this week, however, models are showing that the system will likely slow down around landfall time, prolonging impacts like surge and inland flooding.

Intensity forecast:
The closer Isaac gets to landfall without having formed an eye, the better it is for intensity at landfall. Isaac has strengthened only modestly in the past 24 hours, and is still struggling with a less-than-conducive atmospheric environment. The HWRF remains on the high end of the intensity spectrum, suggesting Isaac will be a weak category 2 upon landfall. Other models suggest it will be a strong category 1, but the difference is splitting hairs. The National Hurricane Center's official forecast is for Isaac to continue strengthening over the next day, reaching category 2 at landfall.


Figure 2. Tide gauge data from St. Petersburg, Florida. The green line shows the storm surge. As Isaac's counterclockwise winds blew offshore this morning, water levels feel two feet at St. Petersburg. The winds switched to onshore this afternoon as the center of Isaac moved more to the northwest, bringing a storm surge of two feet to the city.

Storm surge observations from Isaac
This morning, as Isaac's counter-clockwise winds brought offshore winds to the Tampa/St. Petersburg area, ocean waters fell two feet along the coast. This afternoon, winds have shifted to blow onshore, and a two foot storm surge has been observed at Naples, Fort Meyers, and St. Petersburg on the west coast of Florida. Water levels have also begun to rise along the coast of Louisiana, with a storm surge of 1.5 feet already occurring at Shell Beach on the east side of New Orleans in Lake Borgne.

Angela and Jeff

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Forecast didn't predict a stall, it's crawling at a snails pace, this has to change to forecast at 11
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Product: Air Force Vortex Message (URNT12 KNHC)
Transmitted: 28th day of the month at 12:22Z
Aircraft: Air Force Aircraft (Last 3 digits of the tail number are 306)
Storm Number & Year: 09L in 2012
Storm Name: Isaac (flight in the North Atlantic basin)
Mission Number: 31
Observation Number: 04
A. Time of Center Fix: 28th day of the month at 11:38:20Z
B. Center Fix Coordinates: 27°51'N 88°13'W (27.85N 88.2167W)
B. Center Fix Location: 184 miles (297 km) to the SE (143°) from New Orleans, LA, USA.
C. Minimum Height at Standard Level: 1,224m (4,016ft) at 850mb
D. Estimated (by SFMR or visually) Maximum Surface Wind: 45kts (~ 51.8mph)
E. Location of the Estimated Maximum Surface Wind: 69 nautical miles (79 statute miles) to the WNW (303°) of center fix
F. Maximum Flight Level Wind Inbound: From 42° at 58kts (From the NE at ~ 66.7mph)
G. Location of Maximum Flight Level Wind Inbound: 78 nautical miles (90 statute miles) to the WNW/NW (304°) of center fix
H. Minimum Sea Level Pressure: 977mb (28.85 inHg)
I. Maximum Flight Level Temp & Pressure Altitude Outside Eye: 17°C (63°F) at a pressure alt. of 1,527m (5,010ft)
J. Maximum Flight Level Temp & Pressure Altitude Inside Eye: 21°C (70°F) at a pressure alt. of 1,527m (5,010ft)
K. Dewpoint Temp (collected at same location as temp inside eye): 20°C (68°F)
K. Sea Surface Temp (collected at same location as temp inside eye): Not Available
L. Eye Character: Open from the south-southwest to the north-northeast
M. Eye Shape & Diameter: Circular with a diameter of 50 nautical miles (58 statute miles)
N. Fix Determined By: Penetration, Radar, Wind, Pressure and Temperature
N. Fix Level: 850mb
O. Navigation Fix Accuracy: 0.02 nautical miles
O. Meteorological Accuracy: 1 nautical mile
Remarks Section:
Maximum Flight Level Wind Outbound: 86kts (~ 99.0mph) in the southeast quadrant at 11:57:30Z
Member Since: May 21, 2006 Posts: 5091 Comments: 114758
Quoting weatherh98:
does isaac realize that if he wrapped convectonaround he could be a two or a three?


Isaac like his biblical namesake must be old and senile, I think he keeps forgetting that he is supposed to be a hurricane. Quite okay by me, I like his senility.
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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LAKE CHARLES LA
547 AM CDT TUE AUG 28 2012

.DISCUSSION...
TROPICAL STORM ISAAC VERY CLOSE TO BECOMING A HURRICANE THIS
MORNING...WITH LATEST SAT IMAGERY BEGINNING TO SHOW A RAGGED EYE.
NEVERTHELESS...ISAAC REMAINS A VERY LARGE CYCLONE...WITH TROPICAL
STORM FORCE WINDS EXTENDING 180 NAUTICAL MILES ACROSS THE NE & NW
QUADRANTS OF THE STORM. THUS...TROPICAL STORM FORCE WINDS ALREADY
INFRINGING ACROSS THE FAR SOUTHEASTERN COASTAL WATERS ZONES.
ALSO...ISAAC MADE A SLIGHT WNW JOG OVERNIGHT...WHICH MADE IT
NECESSARY TO ADJUST THE FORECAST TRACK A LITTLE WEST AS WELL.

FOR THE TWO REASONS ABOVE...THE TROPICAL STORM WARNINGS HAD TO BE
EXTENDED WESTWARD TO CAMERON...AND INCLUDES PARISHES FROM RAPIDES...
ALLEN...JEFF DAVIS...AND EASTERN CAMERON EASTWARD TO THE
ATCHAFALAYA RIVER. THE TROPICAL STORM WATCH WAS EXTENDED WESTWARD
TO HIGH ISLAND...INCLUDING JEFFERSON AND ORANGE COUNTIES IN SE TX
ONLY. THE TROPICAL STORM WATCH REMAINS UNCHANGED ACROSS WESTERN
CAMERON...CALCASIEU...BEAUREGARD...AND VERNON PARISHES.

Saw this coming ....as a mariner you can't help but
plot courses for storms too..lol
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2750. ncstorm
From WWAY in wilmington, nc

Tropical moisture streaming effortlessly into SE North Carolina now. Really limitless rain in these setups
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there is the eye..... hes gonna make it.

i live in central lafourche parish the eye of this thing should pass over my house
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Tides are up 4 feet at Shell Beach already per Cantore.
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Quoting RTSplayer:
Wow.

They updated the forward speed to just 6mph...

That changes everything now.

This will give more time for intensification initially, but up-welling may kill it later on.

Worst thing about this is those rainfall totals will come up higher if it stays moving so slowly as it approaches land.




i think this could really ramp up too a cat 2 or 3 storm this is looking more and more likey now
Member Since: May 21, 2006 Posts: 5091 Comments: 114758
2746. GetReal


Closer, almost there for a completely closed in eye wall.
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Quoting Tazmanian:
there is a lot of 80 too 85kt fight level winds being reported now


wow!

The power bleeped out for a few seconds made me nervous!
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2744. WxLogic
Quoting SWLACajun:
What would cause the predicted westward drift?


If it get's caught by the C CONUS High:



Is currently on its periphery.
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Good morning ev1, I see he still not a hurricane. At least this thing isn't a cat 2,3,4 or really a 1. I know the surge might be bad but the wind isn't.He just can't get his act together. Like someone said earlier this is gonna be a rain maker and maybe it will get up in the middle of the U.S. and bring them beneficial rains. Stay safe everyone.

sheri
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Wow.

They updated the forward speed to just 6mph...

That changes everything now.

This will give more time for intensification initially, but up-welling may kill it later on.

Worst thing about this is those rainfall totals will come up higher if it stays moving so slowly as it approaches land.
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Issac looks like he has slowed to a crawl. Not good for the coastal areas of that region (SE La, MS. AL). It's going to be a long and punishing flooding and storm surge event for sure over the next 24-36 hours.
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Quoting FLPandhandleJG:




well from what i can c, that last bit of dry air i saw about an hour ago, looks to be out.. Can Isaac start to build his inner core b4 he hits land.. Well if he keeps slowing down then he might do so.. but it wont be strong in the wind category but def will be some moisture that could dump quite a bit of rain into New Orleans and maybe into sw Alabama..

Send it up my way, we will take all we can get! Recon finding some 80 knot flight level winds in the southwest quadrant of Isaac.
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Question: With the Hurricane center shifted tropical storm watches further west into Texas, does this indicate they are thinking a possible west shift in the track.
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What would cause the predicted westward drift?
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2736. WxLogic
Time is running out for Isaac... low PW about to get injected from the SW:

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2735. Mikla
StormJunkie location and link or link
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Quoting weatherh98:
does isaac realize that if he wrapped convectonaround he could be a two or a three?


Don't tell him.
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The latest goes14 pictures shows convection at the eye getting stronger.
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Quick question - what is causing him to slow down?
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there is a lot of 80 too 85kt fight level winds being reported now
Member Since: May 21, 2006 Posts: 5091 Comments: 114758
close to making me very nervous

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Quoting TcuFrogs:
So I am seeing postings showing a slowing motion, some like Taz is expecting a stall, none which is good for anybody. Still learning how to read the steering maps, are the current maps out yet? One last thing, I know the surface temps of the water is very much like a bath tub, but does the depth of the water in that area also have the temperature, to help this system ramp up?


Steering layer may suggest a potential stall with a slight drift to the west, which the GFS was really spamming that solution two days ago. It was forecasting the storm to be east of NOLA and turn west into the city, that obviously isn't going to happen, but it looks like it may be W or NW of the city and then stall or take an awkward turn.

It may still end up being valid, just shifted a tad to the left for starters.
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Quoting lobdelse81:

Amazing how even these areas of interest way out in the Atlantic also can't seem to get their act together. I mean, look at 97L- it has remained a 30-40% invest for what seems like days now. I wonder what the issue is across the Atlantic Basin? And are we to assume this will continue from here on out.


El Nino may be having more influence than some think. :)
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It looks like Isaac is barely moving on radar, especially in the last hour or so, can't really tell what direction its going because its moving so slow, my best guess would be NW at 310 degrees or so.
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someone explain how its 110 miles from mouth of Mississippi River at 4 AM and at 7 AM its 105 miles from mouth, but the storm is moving 7 MPH right at the mouth of the river. Isaac is moving at a snails pace.
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Quoting SFLWeatherman:
WE now have a ENE!!!
what do you mean?
Member Since: August 16, 2007 Posts: 0 Comments: 397
looks like Isaac is overe the highet
Heat Potential in the gulf

Member Since: May 21, 2006 Posts: 5091 Comments: 114758
does isaac realize that if he wrapped convectonaround he could be a two or a three?
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well from what i can c, that last bit of dry air i saw about an hour ago, looks to be out.. Can Isaac start to build his inner core b4 he hits land.. Well if he keeps slowing down then he might do so.. but it wont be strong in the wind category but def will be some moisture that could dump quite a bit of rain into New Orleans and maybe into sw Alabama..
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Quoting RTSplayer:
It is taking a hard left turn, much like the GFS said yesterday and the day before.

The hard turn is just about a degree or so farther south than originally modeled though.

May come in closer to Houma area.


That's exactly what it looks like to me too.
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tampa..not.much.over.there
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Quoting TropicalAnalystwx13:
97L is back up to 40%, the tropical wave remains at 10%.

TROPICAL WEATHER OUTLOOK
NWS NATIONAL HURRICANE CENTER MIAMI FL
800 AM EDT TUE AUG 28 2012

FOR THE NORTH ATLANTIC...CARIBBEAN SEA AND THE GULF OF MEXICO...

THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON TROPICAL
STORM ISAAC...LOCATED ABOUT 105 MILES SOUTH-SOUTHEAST OF THE MOUTH
OF THE MISSISSIPPI RIVER.

SHOWER ACTIVITY ASSOCIATED WITH AN AREA OF LOW PRESSURE LOCATED
ABOUT 1250 MILES WEST-NORTHWEST OF THE CAPE VERDE ISLANDS IS A
LITTLE MORE CONCENTRATED THIS MORNING. ENVIRONMENTAL CONDITIONS
APPEAR TO BE CONDUCIVE FOR SLOW DEVELOPMENT DURING THE NEXT
COUPLE OF DAYS. THIS SYSTEM HAS A MEDIUM CHANCE...40 PERCENT...OF
BECOMING A TROPICAL CYCLONE DURING THE NEXT 48 HOURS AS THE LOW
MOVES WEST-NORTHWESTWARD TO NORTHWESTWARD AT 10 TO 15 MPH.

A TROPICAL WAVE LOCATED NEAR THE CAPE VERDE ISLANDS IS PRODUCING A
LARGE BUT DISORGANIZED AREA OF SHOWERS AND THUNDERSTORMS.
ENVIRONMENTAL CONDITIONS APPEAR CONDUCIVE FOR SOME GRADUAL
DEVELOPMENT OF THIS WAVE DURING THE NEXT FEW DAYS. THIS SYSTEM HAS
A LOW CHANCE...10 PERCENT...OF BECOMING A TROPICAL CYCLONE DURING
THE NEXT 48 HOURS AS IT MOVES WESTWARD ABOUT 15 MPH.

ELSEWHERE...TROPICAL CYCLONE FORMATION IS NOT EXPECTED DURING THE
NEXT 48 HOURS.

$$
FORECASTER AVILA
told people this was not down or out 97L may become potential Kirk and pre 98L Leslie.
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Good morning. I'm under a tropical storm watch.

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So I am seeing postings showing a slowing motion, some like Taz is expecting a stall, none which is good for anybody. Still learning how to read the steering maps, are the current maps out yet? One last thing, I know the surface temps of the water is very much like a bath tub, but does the depth of the water in that area also have the temperature, to help this system ramp up?
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WE now have a ENE!!!
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Quoting Bobbyweather:
Flight level winds reaching 86 kts (99 mph).


Dr. Lyons' general rule was that kts at flight level normally is the same value in mph at surface observation height, so we may be seeing those winds ramp up now or during the next few hours.

That should correspond to 80 to 85mph wind at the surface either now or in the near future.
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Quoting uncwhurricane85:


you know what i miss.....cat 5 hurricanes


Well IMO, if anymore storms do form, I dont think they will reach that strength, Unless they do get hit by any strong wind shear, dry air, or dealing with land interaction.. Could possibly see a cat 4 in a weak or so if any of those potential storms aren't tamper with.. lol

But anyways.. Issac is still getting beating up by that dry air to the north and still the center is getting tamper with as well.. I think if the dry air wasn't messing with the inner core of Isaac then I c a pretty good cat 3 storm or maybe a tad bit stronger.. But thats not the case..
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Quoting MAweatherboy1:
Flight level winds over 90mph.



man this is not good with this slowing down even more this still has about a full day overe water
Member Since: May 21, 2006 Posts: 5091 Comments: 114758
i noted recon is now finding 80kt fight level winds
Member Since: May 21, 2006 Posts: 5091 Comments: 114758
Flight level winds reaching 86 kts (99 mph).
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It is taking a hard left turn, much like the GFS said yesterday and the day before.

The hard turn is just about a degree or so farther south than originally modeled though.

May come in closer to Houma area.
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2707. GetReal
Quoting WetBankGuy:


All the local mets (yes I watched Bob Breck last night; forgive me) said that had to be a typo/instrument fluke. I've look at all the loops and still don't see anything but that indentation that wants to be an eyewall when it grows up. Current FB joke from NOLA peeps is we should be calling it "saac".

Local private stations report a steady 4 from the north but the trees look more like F4. High cloud cover still broken here in Gentilly at the Fortress of Squalitude (90.4W 29.59 N) Occasional low clouds (< 1,000 ft) headed due south at much more than 4 mph. Pressure 29.55 and steady.




Ditto: My barometer is now down to 29.51 on the Westbank.
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Flight level winds over 90mph.
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2705. Michfan
Good morning everyone. Looks like he finally mixed out all that dry air he had on his east side last night.
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land fall intensity adjustments.

(or lowest pressure since GFDL intensifies some after land fall).

Adjusted 06z GFS 971mb
Adjusted 06z GFDL 967mb
Adjusted 06z HWRF 969mb
Linear trend 971mb (at NOLA)



Maybe it will make 75mph by the time it drops to 971mb...
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Jeff co-founded the Weather Underground in 1995 while working on his Ph.D. He flew with the NOAA Hurricane Hunters from 1986-1990.